CFL

It wasn't until fairly recently that I was overcome with curiosity and decided to see what was inside the base of one of those compact fluorescent lamps (CFL) which are now becoming ubiquitous. The old long tubes are become less common and the need for ballast and starter is obviated by the use of an electronic circuit inside the CFL. I was quite surprised by the amount of components inside. The lamps are relatively expensive compared to ordinary incandescent bulbs but are said to last from 5 to 20 times longer. The components inside seem to be quite useful at first glance and will fill your junk box in time.

An inside view of a typical CFL

The parts after they were removed from the board. This took less than 10 minutes with a soldering iron and solder sucker. The transistors are marked 13003; these are NPN high voltage power switching transistors and the spec sheets are available on the internet. The diodes were mostly 1N4007. There was a useful ferrite ring and a choke, a handful of resistors and capacitors. These components correspond quite closely to those found on the circuit shown below.

The CFL needs to be cut carefully and you should wear eye and hand protection in case of accidents. Actually, the plastic base is relatively thin and easily cut with a craft knife. Just be sure that you don't cut yourself if the knife slips suddenly. You can also saw into the base with a hacksaw blade but you must make a shallow cut to avoid damaging the internals.

Once the base is opened up you can cut the wires leading to the curled fluorescent tube and discard this part. The wires to the screw base can also be cut and the circular circuit board will come out.

The boards come in various sizes depending on the wattage of the CFL and the circuitry is mostly identical but the components on the larger CFL are usually bigger. If you bought the components separately you may well pay more for them than the price of a new CFL! Of course, manufacturers of CFL's get big discounts for bulk purchase of the components.

On the 220VAC input side there are 4 diodes, usually of the 1N4000 series. These are useful for power supply projects. There are also useful electrolytic capacitors and a ferrite ring which can be used in rf projects. There are also power transistors which can be used for other things, see below!

There is a fuse on one of the 220VAC wires and this may look like, or actually be a very low value resistor, or look like a small glass diode. Sometimes it is encapsulated in heat shrink tubing. Check the fuse and if it is open circuit, that may indicate a fault on the board. Repairing a CFL is not very economical but recovering the components is a good idea to save money on future projects. If your CFL has failed quite early in its life it will be likely that the transistors are also damaged. If the CFL has failed due to long use then the electronics are usually intact. If your circuit board is blackened then there is only one place for it! Remove the ferrite ring before tossing the rest in the trash.

There is a project on the internet which uses most of the components inside a CFL to make an 80m CW qrp transmitter! The only extra components required are a crystal and some low pass filter components for the output.

I have made a small collection of these CFL pcb's but they are slow to accumulate because the tubes last quite a long time! Sometimes of course there is a fault in the unit which leads to destruction of the components but generally speaking the CFL board should be still ok when the tube fails. Needless to say you should test the components you remove from the CFL before using them in another project.

73's and long live the amateurs junk box!